The challenges for toddlers (2-3 year olds) in foster care straddle issues faced by infants and preschoolers. Similarly to infants in foster care, toddlers face significant challenges in forming new attachment relationships; similarly to preschoolers, they face challenges developing behavioral control. The attachment needs of these children are not addressed well by an exclusively social learning approach, and the needs for developing behavioral control are not addressed well by an exclusively attachment approach. This competing continuation R01 would assess the effectiveness of an intervention that targets these dual issues within the context of the child welfare system. Attachment and Biobehavioral Catch-up for Toddlers in Foster Care (ABC-T) was developed to help foster parents: provide nurturing care so that children develop secure, trusting relationships; and set reliable contingencies that enhance children's ability to regulate behavior and biology. This intervention's effectiveness will be assessed in a randomized clinical trial. Participants will include 220 young children between the ages of 24 and 36 months who are placed into foster care. Children will be randomly assigned to receive either the ABC-T intervention or a control intervention, Developmental Education for Families (DEF). Both interventions will consist of 10 sessions delivered in families' homes. Foster parents' behaviors and children's functioning will be assessed at pre- and post-intervention, and when children are 3-, 4-, and 5-years old through a variety of tasks. Foster parents receiving the ABC-T intervention are expected to provide more nurturing care and to set more reliable contingencies than foster parents receiving the DEF intervention. Children in the ABC-T intervention group are expected to show more secure attachments to caregivers than children in the DEF intervention, to show more normative production of cortisol, to show fewer behavior problems, and to show lower incidence of DSM IV-R disorders, including most especially Oppositional Defiant Disorder and Conduct Disorder, than children in the DEF intervention group. PUBLIC HEALTH RELEVANCE: Toddlers in the foster care system face unique challenges of forming attachments to new caregivers while learning to control their behavior. However, there are few evidence-based programs that address these issues. Specialized mental health services that specifically target the needs of these children will be assessed in this study.